Field of the Invention
The present invention relates to a multilayer ceramic capacitor whose dielectric layers are constituted by ceramic grains of a specific composition.
Description of the Related Art
In recent years, there is a high demand for smaller electronic components to support increasingly dense electronic circuits used in mobile phones, tablet terminals, and other digital electronic devices, and multilayer ceramic capacitors (MLCC) that constitute these circuits are rapidly becoming smaller in size and larger in capacitance.
The capacitance of a multilayer ceramic capacitor is directly proportional to the dielectric constant of the constitutional material of the dielectric layers constituting the capacitor and also to the number of dielectric layers, and inversely proportional to the thickness of one dielectric layer. Accordingly, meeting the demand for size reduction requires increasing the dielectric constant of the material, while also reducing the thickness of the dielectric layers and thereby increasing the number of dielectric layers.
However, making the dielectric layers thinner increases the voltage applied per unit thickness, which in turn shortens the length of service life of the dielectric layers and reduces the reliability of the multilayer ceramic capacitor. Accordingly, dielectric compositions have been proposed, where donor elements such as Mo and W are added to improve the service life.
Also, Patent Literature 1 describes barium titanate ceramic grains in the form of a dielectric ceramic that gives multilayer ceramic capacitors offering good capacitance temperature characteristics and excellent service life characteristics, characterized in that it has a core and a shell, and contains rare earth element R and M (M is at least one type of element selected from the group that consists of Mg, Mn, Ni, Co, Fe, Cr, Cu, Al, Mo, W and V) as secondary components, where the total concentration of R and M slopes from the grain boundary to the core and becomes minimum in one area and maximum in another area.
In an example provided in the aforementioned literature, a multilayer ceramic capacitor whose dielectric layer is 1 μm thick is produced using a material prepared by adding 0.5 mol of Mn, 0.2 mol of Mo, and 1.0 mol of Gd to 100 mol of barium titanate.